trouble shooting

[Gary]

In your estimation, would the OP be ready for a discussion about TXV's that don't maintain constant superheat? What I'm getting at is that, if a student doesn't yet understand evaporative cooling, which you assumed when you introduced the wet finger scenario, then misbehaving TXV's might be a little too much for that student, eh? Isn't it likely that such a student may not even know what a TXV is? Where's the logical progression in that essay?

Now how did that feel? Ditto! It isn't up to you to decide what a student is ready for. Not that it even matters what the OP is ready for. This isn't his classroom, its a forum.

You wanted to know where my previous post was coming from and its relevence to the thread.

[Gary]

If everyone agreed with me, then by definition I would no longer be a rebel... which would screw up my self-image and spoil all my fun... lol

[sneep]

More accurately, they've fallen upon deaf ears. There's nothing fundamentally flawed in my arguments, I'm quite certain of that.

I disagree.

I've been at this for the better part of thirty years, which is likely longer than you've been alive. Maybe you should start taking that into consideration before showing your ass any more than you already have.

I’ve seen lots of thirty year people who were as knowledgeable as the year they started. The refrigeration cycle hasn’t changed in over a hundred years. Maybe you just need a few more years to flesh out a few areas. I suggest Roy Dossat’s book “Principals of refrigeration”.

Who is they? I believe the discussion has been between you and I. Are you a student?

Students in general. Yes, everyday I’ve been in this trade.

I didn't say that they "did", I only said that they "can". Big difference. Huge difference. I also provided several examples, which you simply don't seem to understand.

I don’t buy your arguments.

[hvacrmedic]

I disagree.


I’ve seen lots of thirty year people who were as knowledgeable as the year they started. The refrigeration cycle hasn’t changed in over a hundred years. Maybe you just need a few more years to flesh out a few areas. I suggest Roy Dossat’s book “Principals of refrigeration”.


Students in general. Yes, everyday I’ve been in this trade.


I don’t buy your arguments.

Given that I once stood in your shoes, I suppose I shall have to take you with a grain of salt.

[hvacrmedic]

It’s common knowledge that the condenser is larger to reject the heat from the evaporator and the superheat picked up on the way back to the compressor and heat of compression.
The leeway current design provides and suction accumalators has escaped you on heat pumps.


Your system is unbalanced and if not a TXV system, you might one day get that set of circumstances that will prove it to you.

Niether are required for a balanced system.

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction. Because you can’t reject heat you can’t pick up.


Pumping down is not a restriction. Overcharging a condenser wasn’t one of the answers. You aren’t making a good argument.


When you know as much as Gary you can lecture about infallibility. You keep saying you don’t agree with him. Maybe some studying will close that gap. Want me to suggest a book? :-)
Cheers

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!

Here are a few of quiz questions for you.

If the suction pressure drops, but head pressure remains constant, will the compressor ampdraw go up, or will it go down?

What happens to the energy supplied to the compressor motor?

Will an evaporator pick up heat from the airstream when the evaporator pressure is 5 psig? 10 psig? 15 psig?

Will a liquid line pick up heat when the liquid line subcooling is zero and it's temperature is below the temperature of the surrounding air?

What will the effect on head pressure be when the condenser's effective internal volume is reduced to 1/4 it's normal operating value by an accumalation of excess liquid refrigerant within it. 1/8 its volume? 1/16 its volume? Etc.

Just a few to get you started in the right direction.

[sneep]

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!

I accept your surrender.

Here are a few of quiz questions for you.
Just a few to get you started in the right direction.

Hvacmedic you need a compressor performance chart and a good book. Not only will those answer your questions. You might actually formulate one interesting enough to discuss.
Cheers

[hvacrmedic]

I accept your surrender.


Hvacmedic you need a compressor performance chart and a good book. Not only will those answer your questions. You might actually formulate one interesting enough to discuss.
Cheers

ROTFLMAO!!!!! You're just too much! It's been fun
Sneep. Just keep at it, you'll get there someday.

[mad fridgie]

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!

Here are a few of quiz questions for you.

If the suction pressure drops, but head pressure remains constant, will the compressor ampdraw go up, or will it go down?

What happens to the energy supplied to the compressor motor?

Will an evaporator pick up heat from the airstream when the evaporator pressure is 5 psig? 10 psig? 15 psig?

Will a liquid line pick up heat when the liquid line subcooling is zero and it's temperature is below the temperature of the surrounding air?

What will the effect on head pressure be when the condenser's effective internal volume is reduced to 1/4 it's normal operating value by an accumalation of excess liquid refrigerant within it. 1/8 its volume? 1/16 its volume? Etc.

Just a few to get you started in the right direction.

Interesting questions, theory and practice can be different depending upon application and equipment type.
On question reduction in suction pressure same head pressure, practically the amperage changes very little (slight drop) on smaller closed couple compressers. This drop is not as great as one would expext, as the volumetric efficiency reduces along with the efficiency of the motor, ( changing the power factor, more amps for Kw drawn or should I say KVA)
For this reason your KW may drop more than the amps indicate.
The evap will pick up heat from the air if the evap is colder. If the evap and air flow remain the same the colder the evap the more energy will be absorbed as long as there is sufficient refrigerant mass flow to absorb the heat. (a bigger compressor is needed)
If the compressor is the same and suction pressure drops then less energy will be absorbed as mass flow will be reduced, with only a small proportion of the evap is actually used for latent heat(boiling of refrigerant) transfer. Refrigerant vapour superheating will occur.
If the air is warmer than the liquid line it will pick up energy regardless if it is sub cooler or not. If there is no sub cooling then flash gas will occur, which then increase liquid line pressure drop which futher increase flash gas.
Condensor presuming all points within the system remain constant, then reduction in volume, thus heat transfer surface area, then head pressure will rise.

[hvacrmedic]

Interesting questions, theory and practice can be different depending upon application and equipment type.
On question reduction in suction pressure same head pressure, practically the amperage changes very little (slight drop) on smaller closed couple compressers. This drop is not as great as one would expext, as the volumetric efficiency reduces along with the efficiency of the motor, ( changing the power factor, more amps for Kw drawn or should I say KVA)
For this reason your KW may drop more than the amps indicate.
The evap will pick up heat from the air if the evap is colder. If the evap and air flow remain the same the colder the evap the more energy will be absorbed as long as there is sufficient refrigerant mass flow to absorb the heat. (a bigger compressor is needed)
If the compressor is the same and suction pressure drops then less energy will be absorbed as mass flow will be reduced, with only a small proportion of the evap is actually used for latent heat(boiling of refrigerant) transfer. Refrigerant vapour superheating will occur.
If the air is warmer than the liquid line it will pick up energy regardless if it is sub cooler or not. If there is no sub cooling then flash gas will occur, which then increase liquid line pressure drop which futher increase flash gas.
Condensor presuming all points within the system remain constant, then reduction in volume, thus heat transfer surface area, then head pressure will rise.

Ok. Good stuff. Now let's put some numbers to this.
I've attached a couple of performance calcs that for the sake of this argument should suffice. The first shows a typical 10 SEER 3 ton A/C system running under moderate conditions. We'll let the conditions be 23.9°C (75°F) return air temp, and 26.7°C (80°F) ambient.

Looking at performance calc #1, which represents the system before a restriction occurs, the condenser heat load contributed by the electrical input works out to about 7.609 btu/hr. The cooling capacity is 36,500, so the total condenser load is about 44109 btu/hr.

Looking at performance calc #2, which represents the system with a LL restriction introduced near the LL service valve, we similarly get a total condenser load of about 21,440 btu/hr.

As you can see, the condenser heat load ratio is approximately 2 to 1. Thus, if we can arrange for the effective condenser area to be reduced by the same ratio by introducing this restriction, then we will have satisfied the conditions required in order to produce the respective sets of system pressures represented in these two performance calcs. In this case the head pressure remains unchanged. In order to get the head pressure to increase after the restriction is introduced, we need only reduce the effective condenser are to a little less than half its original value.

With a long line set, this is not only possible, but again, I have witnessed the effect with my own eyes.

[hvacrmedic]

This is a repost. My apologies, I forgot to upload the attachments. I still don't have an edit button available. Does anyone know how to go about getting one of those?

Ok. Good stuff. Now let's put some numbers to this.
I've attached a couple of performance calcs that for the sake of this argument should suffice. The first shows a typical 10 SEER 3 ton A/C system running under moderate conditions. We'll let the conditions be 23.9°C (75°F) return air temp, and 26.7°C (80°F) ambient.

Looking at performance calc #1, which represents the system before a restriction occurs, the condenser heat load contributed by the electrical input works out to about 7.609 btu/hr. The cooling capacity is 36,500, so the total condenser load is about 44109 btu/hr.

Looking at performance calc #2, which represents the system with a LL restriction introduced near the LL service valve, we similarly get a total condenser load of about 21,440 btu/hr.

As you can see, the condenser heat load ratio is approximately 2 to 1. Thus, if we can arrange for the effective condenser area to be reduced by the same ratio by introducing this restriction, then we will have satisfied the conditions required in order to produce the respective sets of system pressures represented in these two performance calcs. In this case the head pressure remains unchanged. In order to get the head pressure to increase after the restriction is introduced, we need only reduce the effective condenser are to a little less than half its original value.

With a long line set, this is not only possible, but again, I have witnessed the effect with my own eyes.

[mad fridgie]

If we presume that the restriction has cause the head pressure to remain the same "flooding the condensor with liquid" then you have made a mistake in your calculations. This being the case you would have increased liquid sub-cooling.
We all know in refrigeration at time very strange things can happen, I think if i saw what you are describing and would sumise that the system was "slightly" overcharged originally.
With the simulations given, under normal circumstance I would expect the head pressure to fall. (full floating head pressure)

[hvacrmedic]

If we presume that the restriction has cause the head pressure to remain the same "flooding the condensor with liquid" then you have made a mistake in your calculations. This being the case you would have increased liquid sub-cooling.
We all know in refrigeration at time very strange things can happen, I think if i saw what you are describing and would sumise that the system was "slightly" overcharged originally.
With the simulations given, under normal circumstance I would expect the head pressure to fall. (full floating head pressure)

Is this what you meant? (See attachment: performance3.jpg)

That correction actually enhances my argument. And as you can see, it provides very little change to the numbers.

FWIW, Carrier did not include the warning about excessive head pressure (during pump-down conditions with long line sets) as a result of mistaken notions, or as a result of incorrect math. It's an empircal fact that when refrigerant migrates out of the evaporator and in some cases also the LL (and accumulator if applicable), then it is necessarily piled up in the condenser.

A 150 ft lineset with 3/8" LL requires an additional weighted charge of 5 lb. If the system's factory charge is 5 lb, then the system now contains twice its factory charge. If 5 lb of that 10 lb total charge ends up in the condenser due to a LL restriction, then what percentage of the condenser coil will be available to desuperheat and condense the incoming vapor?

I hope you aren't expecting a live demonstration of this effect, because I'm not quite interested enough in convincing any of you. I suggest instead that some of you volunteer to provide a sound argument forbidding an increase in head pressure with a LL restriction. "I can't see it happening" is somewhat less than a valid argument.

Though I once argued from Gary's position, and I'm sure that I argued that position with him in the same thread on an occasion or two, I cannot be convinced now that this effect cannot occur. I've seen it in person, how do you expect me to argue against that, or to take seriously any argument to the contrary?

[Gary]

A rise in head pressure presumes the condenser capacity is insufficient for the heat absorbed in the evaporator. So... there are two factors involved, i.e. condenser capacity and heat load.

Given the absence of a receiver, a restriction might back liquid up into the condenser (more likely if overcharged)... but that same restriction should reduce the heat absorbed in the evaporator.

How is that evaporator heat load maintained?

[mad fridgie]

Is this what you meant? (See attachment: performance3.jpg)

That correction actually enhances my argument. And as you can see, it provides very little change to the numbers.

FWIW, Carrier did not include the warning about excessive head pressure (during pump-down conditions with long line sets) as a result of mistaken notions, or as a result of incorrect math. It's an empircal fact that when refrigerant migrates out of the evaporator and in some cases also the LL (and accumulator if applicable), then it is necessarily piled up in the condenser.

A 150 ft lineset with 3/8" LL requires an additional weighted charge of 5 lb. If the system's factory charge is 5 lb, then the system now contains twice its factory charge. If 5 lb of that 10 lb total charge ends up in the condenser due to a LL restriction, then what percentage of the condenser coil will be available to desuperheat and condense the incoming vapor?

I hope you aren't expecting a live demonstration of this effect, because I'm not quite interested enough in convincing any of you. I suggest instead that some of you volunteer to provide a sound argument forbidding an increase in head pressure with a LL restriction. "I can't see it happening" is somewhat less than a valid argument.

Though I once argued from Gary's position, and I'm sure that I argued that position with him in the same thread on an occasion or two, I cannot be convinced now that this effect cannot occur. I've seen it in person, how do you expect me to argue against that, or to take seriously any argument to the contrary?

Thats the nature of our game, occassionally things happen out of the ordinary. I would never say that a restriction in the LL is an impossible cause of increased head pressure, but to claim it as a normal condition is in itself flawed.
So if I ask the question what is "most likely" to raise head pressure
An increased air "on" (ambient) to the condensor or
A restricted liquid line.
I suspect when you have seen this occur, you had high ambients and a high evap heat load (this would be normal if a fault has occurred), then other factors come into play, increased compressor power draw, reduced condensor efficiency due to air density and its thermal properties.

[hvacrmedic]

Thats the nature of our game, occassionally things happen out of the ordinary. I would never say that a restriction in the LL is an impossible cause of increased head pressure, but to claim it as a normal condition is in itself flawed.
So if I ask the question what is "most likely" to raise head pressure
An increased air "on" (ambient) to the condensor or
A restricted liquid line.
what would your answer be

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.

Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:

"C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions."

"To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer."

"Stretching the argument, as I did above, is an example of what not to do on a multiple choice question."

In response to Sneep:

"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"

"I didn't say that they "did", I only said that they "can". Big difference. Huge difference."

[mad fridgie]

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.

Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:

"C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions."

"To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer."

"Stretching the argument, as I did above, is an example of what not to do on a multiple choice question."

In response to Sneep:

"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"

"I didn't say that they "did", I only said that they "can". Big difference. Huge difference."

Mad boi, if that doesn't clear it up for you, then pardner, you are just S.O.L.

S.O.L ? a compliment??

[Gary]

A rise in head pressure presumes the condenser capacity is insufficient for the heat absorbed in the evaporator. So... there are two factors involved, i.e. condenser capacity and heat load.

Given the absence of a receiver, a restriction might back liquid up into the condenser (more likely if overcharged)... but that same restriction should reduce the heat absorbed in the evaporator.

How is that evaporator heat load maintained?

To take this a step further:

The same restriction that is reducing the condenser capacity should be starving the evap and thus reducing its capacity to match the condenser... and your attachments seem to agree.

If there is enough refrigerant to maintain the evaporator capacity while at the same time backing up into the condenser and reducing its capacity, well... that would pretty much be the definition of an overcharged system.

I wouldn't go so far as to say that it can't happen. After all, you have seen it with your own eyes. Can't argue with that.

Maybe a long line set can make the difference. Possibly the liquid line could function as an extension of the evaporator... keeping the evap load up?

Stranger things have happened.

[sneep]

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.
Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:

You haven’t been right yet. Restating it doesn’t make your points true.

In response to Sneep:
]"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"

I asked you to expound on what you said. To clarify what you mean’t. You did and I called you on it because it’s wrong.

Mad boi, if that doesn't clear it up for you, then pardner, you are just S.O.L.

Your charts only show what the output of your compressor is based on the input you put in. Garbage in is garbage out.
It does not show the results of a restriction. Thats not the purpose of that calculator.
You fail to grasp what everyone is saying.
1. When you introduce a restriction you reduce the refrigerant getting to the evaporator.
2. Less refrigerant in the evaporator means you can’t pick up as much heat.
3. That means less to reject in the condenser.
4. Temperature goes down, pressure goes down.

Backing the refrigerant up into the condenser from a restriction and adding long lines with the extra charge it takes to fill them will not maintain a increase in head pressure beyond what it takes to stabize the system to the feed rate of the restriction. If you can’t pick up the heat you won’t have it to reject.

You might want to chew on what has been said before you post again.

Cheers

[hvacrmedic]

Backing the refrigerant up into the condenser from a restriction and adding long lines with the extra charge it takes to fill them will not maintain a increase in head pressure beyond what it takes to stabize the system to the feed rate of the restriction. If you can’t pick up the heat you won’t have it to reject.

You might want to chew on what has been said before you post again.

Cheers

You haven't listened to a word thus far, nor are your replies very coherent in general. Your grasp of thermodynamics is not adequate enough for you to formulate a valid argument on your own. I don't expect that I can fix that for you, so I'm going to have to depart from the conversation. Cheers.

[hvacrmedic]

To take this a step further:

The same restriction that is reducing the condenser capacity should be starving the evap and thus reducing its capacity to match the condenser... and your attachments seem to agree.

The attachments paint a different picture than you're seeing Gary. Though the cooling capacity has dropped to just over 1/3, the condenser heat load has dropped to 1/2. The changes in the two loads are not self canceling as you have presumed. You're ignoring the compressor kw component, which according to the performance calcs, has not changed at all in this instance.

Nor does the amount of refrigerant in the evaporator relate directly to the cooling capacity of the evaporator coil. I suppose that with a saturated suction temperature of 1°F and pressure of 25psig, the same lb of R22 might be able to absorb more heat than it did at 41°F and 70psig. At half capacity, the evaporator coil has less than half the initial mass of refrigerant within it. Just a thought.

[hvacrmedic]

S.O.L ? a compliment??

S = "fill in the blank"
O = out of
L = luck.

HTH.

H = hope
T = this
H = helps.

[hvacrmedic]

The attachments paint a different picture than you're seeing Gary. Though the cooling capacity has dropped to just over 1/3, the condenser heat load has dropped to 1/2. The changes in the two loads are not self canceling as you have presumed. You're ignoring the compressor kw component, which according to the performance calcs, has not changed at all in this instance.

Nor does the amount of refrigerant in the evaporator relate directly to the cooling capacity of the evaporator coil. I suppose that with a saturated suction temperature of 1°F and pressure of 25psig, the same lb of R22 might be able to absorb more heat than it did at 41°F and 70psig. At half capacity, the evaporator coil has less than half the initial mass of refrigerant within it. Just a thought.

Sorry, I buggered that up a little bit. Though the refrigerant will absorb more btu/lb at the lower pressure, it is a negligable change. What I meant was that it will abosb heat a much greater rate, due to the higher temperature differential. Half of a coil at 1° F will absorb, per unit time, more heat than a fullly saturated coil at 41° F. Since the cooling capacity of the coil is only 1/3 the initial value, it should follow that the saturated portion of the coil has dropped to much less than 1/3 of the total, leaving less than 1/3 the initial refrigerant mass in the coil.

All of this is immaterial though. Even if these things scaled differently than in my example, it would still be possible to for a high head pressure with a restriction. One would need only reduce the size of the condenser coil relative to the evaporator. In refrigeration systems this is not an uncommon condition, which I presume is one of the many reasons for using a receiver on those systems. That was in turn one of your initial counterarguments, was it not, that the reciever would prevent this?

[Gary]

Sorry, I buggered that up a little bit. Though the refrigerant will absorb more btu/lb at the lower pressure, it is a negligable change. What I meant was that it will abosb heat a much greater rate, due to the higher temperature differential. Half of a coil at 1° F will absorb, per unit time, more heat than a fullly saturated coil at 41° F. Since the cooling capacity of the coil is only 1/3 the initial value, it should follow that the saturated portion of the coil has dropped to much less than 1/3 of the total, leaving less than 1/3 the initial refrigerant mass in the coil.

All of this is immaterial though. Even if these things scaled differently than in my example, it would still be possible to for a high head pressure with a restriction. One would need only reduce the size of the condenser coil relative to the evaporator. In refrigeration systems this is not an uncommon condition, which I presume is one of the many reasons for using a receiver on those systems. That was in turn one of your initial counterarguments, was it not, that the reciever would prevent this?

Logically then, the greater the restriction, the higher the head pressure would go... and a pumpdown would send the head pressure right up through the roof. Possibly the extended liquid line could hold enough extra liquid to completely fill the condenser?

I'm thinking the manufacturers have a limit on how far the liquid line can be extended. Maybe this is why?

[hvacrmedic]

Logically then, the greater the restriction, the higher the head pressure would go... and a pumpdown would send the head pressure right up through the roof. Possibly the extended liquid line could hold enough extra liquid to completely fill the condenser?

I'm thinking the manufacturers have a limit on how far the liquid line can be extended. Maybe this is why?

Yes, the total charge can be easily be too large for the condenser coil to accomodate.

NOTE
: All outdoor unit coils will hold only factory supplied
amount of refrigerant. Excess refrigerant, such as in long line
applications, may cause unit to relieve pressure through internal
pressure relief valve (indicated by sudden rise of suction pressure)
before suction pressure reaches 5 psig (35kPa). If this occurs, shut

unit off immediately, front seat suction valve, and recover

remaining pressure.

[nevgee]

[quote=sneep;188124]

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction.


Did I miss something here?

High pressure is high pressure, doesn't make any difference whether its hydraulic or a gas or a bag of exited aliens... high pressure is High pressure.

[bmundoorkote]

1.filter drier chokeup.
2.cond:fan not working if air cooled
3.cond;coil clogged up with dirt
4.ambient temp.very high

[sneep]

[QUOTE=nevgee;188401]

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction.


Did I miss something here?

High pressure is high pressure, doesn't make any difference whether its hydraulic or a gas or a bag of exited aliens... high pressure is High pressure.

So along that line of thought.... Overcharging doesn't raise head pressure once the liquid line is full?

[little turtle]

I agree c would be the answer but would a restriction in the liquid line cause liquid stackin in the condensers possibly raising head

in normal charge, restriction in the liquid line will not increase head pressure.
Like pump down system, due to decrease in refrigerant flow to the evaporator (it seems lower cooling capacity), the head pressure will slightly decrease too.